Hello Joseph,
Profit = Revenue - Cost
We need to find an equation for the revenue R(x).
R(x) = number of units * unit price = x * p(x) = x(72-x) = 72x - x2
Therefore: Profit P(x) = 72x - x2 - (250 + 52x) = - x2 + 20x -250
To find max profit, run the 1st derivative test, so set P'(x) = 0 and solve for x:
P'(x) = -2x + 20
set P'(x) = 0 ----> -2x+20 = 0 ----> -2x = -20 -----> x = 10
The number of units, x, that produces the maximum profit is 10.
Cheers.